In order to prevent damage to the gears, it is necessary to synchronize the driving and driven members when shifting from one gear to the next. In motor vehicles in which such synchronization is not carried out automatically, the driver must, by suitable control of the gas pedal reduce the speed of the engine when shifting from a lower gear to a higher gear and must increase the speed of the engine when shifting from a higher to a lower gear. This control requires a certain amount of skill on the part of the driver and tends to distract his attention from the traffic conditions. Therefore a number of mechanical synchronization systems have been proposed which operate without intervention of the driver. However, such mechanical arrangements cannot be incorporated into all vehicles. For example in heavy duty trucks it is almost impossible to incorporate such arrangements, in particular with respect to the lower gears.
An electro-mechanical system is known from DT-OS No. 1,655,210 in which the engine is automatically braked when a gear shift from a lower to a higher gear takes place. British Pat. No. 1,466,867 discloses the system in which a fuel injection pump is controlled during gear shift operations.